Impedance tuners are often used for testing, tuning and calibration of electronic devices. Also, impedance tuners are the most common method for radio frequency (RF) and microwave (MW) amplifiers to be tested for measurement of performance. Impedance tuners can be used on load-pull and noise measurements at microwave and millimeter-wave frequencies.
An impedance tuner includes a transmission line, such as a slabline, coaxial line, or waveguide. Placement of capacitive objects such as probes along the transmission line alters the impedance or electronic profile seen by the device under test (DUT) which is connected or coupled to the tuner transmission line. The object may be placed axially along the transmission line to affect the phase, while movement of the object transverse to the transmission line will alter impedance magnitude or gamma effects. In automated tuners, motors are used to position the capacitive objects along the transmission line and transverse to the transmission line.
Multi-harmonic automated tuners incorporate multiple carriages to perform measurements on both the fundamental frequency and harmonic frequency simultaneously. The fundamental frequency is the basis for the multi-harmonic automated tuners. A harmonic frequency is a multiple of the fundamental frequency whose cycle fits within the span of the fundamental frequency cycle. An example would be the 2nd harmonic, which completes two frequency cycles within the time of one fundamental frequency cycle.
Setting different impedance points at a harmonic frequency cannot be done with the same carriage used to set the fundamental frequency impedance points. Therefore, adding additional carriages is needed. An impedance tuner with two carriages can set impedances independently at two frequencies, i.e. the fundamental frequency and a harmonic frequency. Similarly, an impedance tuner with three carriages can set impedances independently at three frequencies, i.e. the fundamental frequency and two harmonic frequencies. Each additional carriage allows one additional frequency to be tuned independently. However, adding additional carriage units will add drive unit components (i.e. motor, lead screw, lead screw nut), so manufacturing the tuner in a space confined area becomes more of a challenge. Each carriage needs to be controlled for position separately, yet accurately in ratio to the first carriage. By adding additional drive components, variables are added that may not allow the movement of one carriage to be in synchronization with another carriage.